The Sensory Motor Performance Program specializes in the study of human motor control in normal and impaired subjects. Current projects examine upper limb, lower limb, neck, and eye movements using a combination of experimental and computer-based analysis. This proposal requests a graphics supercomputer to enhance our experimental and computational studies, and to link our investigative teams via a high speed computer network. This advanced technology will make possible the development of three-dimensional (3D) computer graphics models of the musculoskeletal system, which will significantly enhance our studies of movement control. Specifically, Drs. Peterson and Keshner will use the computer to develop detailed computer graphics models of the head and neck musculature as an extension of their study of human neck movement. This project seeks to examine how the array of neck muscles are activated in order to better understand the. neural control system in normal subjects as well as those that have undergone labyrinthectomies. Developing computer models will complement their experimental work by quantifying the torque-generating characteristics of the muscles responsible for stabilization of the head. Dr. Buchanan's investigation of static arm postures will also be greatly enhanced by developing a 3D graphics model of the human upper limb. This model will be used as the basis for a set of experimental and theoretical investigations of the neurophysiology underlying the maintenance of steady postures. Dr. Delp will study the biomechanical consequences of several musculoskeletal reconstructions that are performed on patients with neurological impairments, such as stroke and cerebral palsy. The graphics supercomputer will enable Dr. Delp to create models of individual patients based on data from medical imaging equipment. These models will be manipulated on the computer display to explore how surgical alterations of the musculoskeletal system affect muscle strength. Dr. Keshner, in her study of postural control, will use the workstation to animate 3D motion data and to overcome the major limitation of her current experimental arrangement-the delay time between collection and analysis of data. This will permit her to select postural perturbations most relevant to the subjects instantaneous musculoskeletal arrangement. With this new capacity, she will investigate the hypothesis that the position of the center of mass with respect to the base of support is the controlled parameter about which all body segments are automatically organized given the appropriate sensory and motor command. Dr. Rymer's studies of spasticity and neuromuscular fatigue aim to quantify how the mechanical properties of muscle are altered by neurological disease and fatigue. These studies rely on accurate modeling and simulation of limb muscle architecture, limb motion trajectories, limb impedance and control strategies, and would be greatly enhanced by the advanced computational capacity of the proposed computer.